HS Football with 2 cameras???

For daytime games (JV football) I use a handheld 7D with 70-300L 4/5.6 and just adore it. Really tack sharp! But, once the sun goes down the 70-300 is just too slow and I put a 15-85 on the 7D for sideline shots and team huddles (at 3200) and use a 5DIII with 70-200 (sadly a I not II) at 6400 for action. The photos I have tried to attach have been 'flickr'd' but show what the 5DIII can do at 6400....some of these shots would've been better (diving catch) with a 300mm 2.8 as I wouldn't have needed to crop but then I would've missed the two other shots (one in the back of the end zone and the other near the sideline) and neither would have been wide enough for the team shots (even on 5DIII).

I use both cameras handheld...because I don't know any better. I don't lose many to shake...but I do keep shutter at 1/800. This may not answer your questions, as both the lenses I use are wider than you're proposing. I hope the comments help anyway.